Helical conveyor systems

ABSTRACT

A helical conveyor system in a freezing unit, wherein cold air from an evaporator (20) is fan-forced upwardly through the turns of the conveyor mesh, a primary cold air flow (26) is directed upwardly through the turns of the conveyor mesh, and a secondary flow (28) of cold air is incident on the top turn of the helix. This has the advantage that the coldest air impinges on the product while the latter is still at its warmest.

This invention relates generally to a helical conveying system and moreespecially to a controlled air flow arrangement for use in a helicalconveying system employed for food freezing.

Helical conveying systems are commonly used in industrial food freezingunits. The food product to be frozen is loaded on to the conveyor priorto entry of the conveyor into the bottom of its helical conveying path,is frozen whilst being conveyed upwardly along the helical conveyingpath, and is removed from the conveyor after the conveyor leaves thehelical conveying path at the top of the helix. For freezing the productwhilst being conveyed in the helical conveying path, it is exposed tocold air circulating within the freezing unit in which the helicalconveying path is located. The conveyor is typically endless, andreturns to the bottom of the helix outside the freezing unit.

A typical belt is of flexible wire mesh, and usually the cold air isblown through the conveyor, over its helical conveying path, from top tobottom of the helix, directly contacting the product to be frozen as itpenetrates downwardly through the successive tiers or turns of theconveyor mesh.

Known controlled air flow arrangements are generally inefficient, andcontrol of the flow of cold air is relatively elementary, so thatturbulence sometimes occurs in the generally downward path of the airflow, leading to unreliable and non-uniform freezing of the product.

It is a general aim of this invention to provide a helical conveyingsystem with an improved cold air flow arrangement.

According to the invention, there is provided a helical conveyor systemin a freezing unit, wherein cold air from an evaporator is fan-forcedupwardly through the turns of the conveyor mesh, a primary cold air flowis directed upwardly through the turns of the conveyor mesh, and asecondary flow of cold air is incident on the top turn of the helix.

Preferably the secondary flow passes downwardly through the upper fewturns of the helix, both primary and secondary flows emerging from theside of the helical conveying path for return to the fans andevaporator. In this case shutter means is preferably provided at theexit of the air flow from the side of the helical conveying path.

A preferred conveying system utilises a drum or capstan located on theinside of the helix to drive the conveyor mesh in its helical path. Inthe preferred arrangement, the secondary air flow passes upwardlythrough the drum to emerge at the top thereof and be diverted radiallyoutwardly and downwardly to be incident on the top turn of the helix. Asecondary shutter means, for example in the form of an adjustable ringdiaphragm, may be provided beneath the bottom turn of the helix tocontrol the relative amounts of air in the primary and secondary flows.Upstream of the secondary shutter means, a closable baffle may beprovided for completely closing off air flow from the evaporator, forexample to enable defrosting.

The invention has the advantage that the coldest air direct from theevaporator impinges on the product whilst the latter is still at itswarmest, i.e. at the bottom of the helix, rapidly sealing in moisture inthe product, reducing dehydration and increasing yield. Moreover, theair flow can be quantitatively controlled to suit the product beingfrozen. The secondary air flow, of air still near to its coldest,ensures that the product is fully frozen immediately before leaving thefreezing unit.

A helical conveyor system in accordance with the invention is nowdescribed by way of example with reference to the accompanying drawing,the single figure of which shows the system diagrammatically from theside, as seen from the interior of a freezer unit.

The freezer unit in which the system is incorporated is basically aclosed housing 10, with entrance 12 for the conveyor and exit 14 for theconveyor. The housing 10 also has various not shown access doors.

The conveyor is an endless flexible wire mesh belt, for example of theAshworth type. Within the freezer unit, it follows a helical path theturns or tiers of which are referenced 16, the belt entering the helixat the bottom and leaving it at the top. The belt has a return path (notshown) from top to bottom outside the freezer unit.

A food product to be frozen is loaded on to the conveyor at the entrance12, and the frozen product is removed from the conveyor at exit 14. Theproduct is frozen in the course of its path along the helical upwardpath of the conveyor belt within the freezer unit, and for this purposeis chilled by a flow of cold air. This air is caused to circulate incontrolled manner within the freezer unit by means of a fan 18 which isassociated with an evaporator 20, both installed within one side of thehousing 10.

In the context of this invention, the helical path conveying system maytake any one of several different forms. Preferably, however, and asillustrated, it is driven in its helical path by a rotating capstan ordrum 22 mounted within the helix, with or without use of a supplementarydriving means at the return path outside the freezer unit. The belt maybe supported by a helical guide at the outside edge of the helix. inconjunction with cantilever arms extending inwardly from the guide tosupport the belt across its full width at appropriate intervals alongits helical path of movement. Alternatively, a simple guide rail may beprovided at the outside edge of the helix, the belt having spacer platesat its inside edge whereby any one turn of the helix is, at said insideedge, supported by the turn next below. As a further alternative theoutside edge of the helix may be supported by spacer plates which areapertured to allow the passage of cold air. In each case, thearrangement is such that the helix is open to the exterior between itsturns, at the outside edge.

The drum 22 may drive the belt directly, or via a narrow supplementaryconveyor which is self-supporting by means of spacers and which in turndrives the inner edge of the product conveyor, and which may at the sametime support the inner edge of the product conveyor.

This invention is concerned, more especially, with an arrangement forcontrolling the cold air flow which freezes the food product in courseof its helical path of movement.

In accordance with the invention, the cold air emergent

evaporator 20 enters a space 24 beneath the conveyor helix and drum, andimpinges directly on the lowest turn of the helix, thence to pass aprimary air flow 26 upwardly through the turns of the wire mesh belt. Asecondary air flow 28 passes upwardly through the inside of the drum.

In order to maintain separation between the primary and secondary airflows, 26, 28, the drum may have a solid internal wall surface. However,if the conveyor belt is self-supporting by spacer plates at its insideedge, these plates may themselves be sufficient to define a closed wallto the outside edge of the conveyor, in which case it is not essentialfor the drum to have a closed cylindrical wall.

The secondary air flow emerges into a space 30 above the drum and,within said space, is turned radially outwardly and downwardly toimpinge on the top turn of the helix. The primary and secondary airflows thence emerge together, from the open outside edge of the helix, afew turns below the top thereof, into an annular space 32, from there tobe drawn back through the fan 18 to the evaporator 20.

A shutter means 34 in the space 32, in practice taking the form ofarcuately segmental plates vertically adjustable between T-bars, forexample, enables the total air flow to be quantitatively controlled. Asupplementary shutter 36 in the space 24, for example in the form of anadjustable ring diaphragm, enables the relative amounts of air in theprimary and secondary flows to be quantitatively adjusted.

Conveniently, a hinged baffle 38 is also provided for shutting off thespace containing the conveyor system from the evaporator exit, forexample to facilitate de-frosting.

The shutter means 34, diaphragm 36 and baffle 38 may be manuallyadjustable or may be power controlled.

When the above-described system is in use, the air first incident on theproduct, at the bottom turn of the helix, is very cold air direct fromthe evaporator, so that the outside layer of the product is very quicklyfrozen to seal moisture inside and avoid risk of product dehydration.Moreover, the air incident on the product at the top turn of the helix,just before the product emerges from the freezer unit, is also very coldair, and acts to ensure that the product is fully frozen. The shutters34, 36 ensure that the air flow can be closely controlled to suit anyspecific product being handled. It is also found that the carefullycontrolled air path flows do not give rise to turbulence which can leadto non-uniform product treatment.

Various modifications of the above-described and illustrated arrangementare possible within the scope of the invention as hereinbefore defined.

We claim:
 1. A helical conveyor system for cooling or freezing a productcomprising:a conveyor for conveying the product, said conveyor includinga belt in a form of a helix with a plurality of turns and having a topand a bottom; a housing enclosing the conveyor, said housing having sidewalls and a top and a bottom; refrigeration means for providing coldair; flow path means in communication with said refrigeration means forintroducing a flow of cold air to both the bottom and top of theconveyor simultaneously, to thereby provide two-sided cooling of theproduct as it is transported from the bottom of the conveyor to the top;and exit means formed in the housing through which the cold air can flowafter it passes over the product.
 2. A helical conveyor system forcooling or freezing a product comprising:a conveyor for conveying theproduct, said conveyor including a belt in a form of a helix with aplurality of turns and having a top and a bottom; a housing enclosingthe conveyor, said housing having side walls and a top and a bottom;refrigeration means for providing cold air; primary flow path means incommunication with said refrigeration means for directing a primary flowof cold air into the housing and upwardly from the bottom of theconveyor through turns of the conveyor; secondary flow path means incommunication with said refrigeration means for directing a secondaryflow of cold air along a flow path different than the primary flow path,the secondary flow being introduced to the conveyor adjacent the top ofthe conveyor; and exit means formed in the housing through which thecold air flows after it has been directed along the primary andsecondary flow paths.
 3. The system of claim 2 wherein said secondaryflow path means causes the secondary flow to pass over the top of theconveyor and downwardly through a few upper turns of the conveyor to aposition where the secondary and primary flows merge.
 4. The system ofclaim 3 wherein said exit means comprises an opening formed in the sideof the housing through which the merged primary and secondary flows exitfrom said housing.
 5. The system of claim 4 further comprising means forselectively controlling the air flow through said opening in the side ofthe housing.
 6. The system of claim 2 further comprising means forcontrolling the primary and secondary flows of cold air.
 7. The systemof claim 6 wherein said controlling means includes a first selectivelyvariable device for controlling flow into said housing, said devicebeing positioned below the bottom of said conveyor.
 8. The system ofclaim 7 wherein said controlling means further includes a selectivelyvariable flow device positioned between the bottom of said conveyor andthe bottom of said housing.
 9. The system of claim 8 wherein saidselectively variable flow device comprises an adjustable ring diaphragm.10. The system of claim 6 wherein said controlling means includes aselectively variable flow device positioned between the bottom of saidconveyor and the bottom of said housing.
 11. The system of claim 6wherein said controlling means includes a selectively variable flowdevice associated with said exit means to vary the flow through saidexit means.
 12. The system of claim 11 wherein said selectively variableflow device associated with said exit means includes an arcuatelysegmental device.
 13. The system of claim 2 further comprising means forclosing off the flow of cold air from the refrigeration means to thehousing.
 14. The system of claim 2 wherein said secondary flow pathmeans includes a vertical conduit formed at the center of the conveyorand extending along the conveyor's axial length.
 15. The system of claim2 wherein the conveyor is driven by a centrally located rotating drum,said drum providing part of said secondary flow path means.
 16. Thesystem of claim 2 wherein said belt includes a plurality of aperturesthrough which air can flow.
 17. A helical conveyor system for cooling orfreezing a product comprising:a conveyor for conveying the product, saidconveyor including a belt in the form of a helix with a plurality ofturns and having a top and a bottom; a housing enclosing the conveyor,said housing having side walls and a top and a bottom; refrigerationmeans for providing cold air; primary flow path means in communicationwith said refrigeration means for directing a primary flow of cold airinto the housing and upwardly from the bottom of the conveyor throughturns of the conveyor; secondary flow path means in communication withsaid refrigeration means for directing a secondary flow of cold airalong a flow path different than the primary flow path to the top of theconveyor and downwardly through a plurality of upper turns of theconveyor where the secondary flow merges with said primary flow; andexit means formed in a side wall of the housing through which the coldair flows out of the housing.
 18. The system of claim 17 furthercomprising,a first selectively variable device for controlling flow intosaid housing, said device being positioned below the bottom of saidconveyor; and a second selectively variable flow device associated withsaid exit means to vary the flow through said exit means.
 19. The systemof claim 17 wherein said belt includes a plurality of apertures throughwhich air is flowable.
 20. A helical conveyor system for cooling orfreezing a product comprising:a conveyor for conveying the product, saidconveyor including a belt in the form of a helix with a plurality ofturns and having a top and a bottom; a housing enclosing the conveyor,said housing having side walls and a top and a bottom; refrigerationmeans for providing cold air; primary flow path means in communicationwith said refrigeration means for directing a primary flow of cold airinto the housing and upwardly from the bottom of the conveyor throughturns of the conveyor; secondary flow path means in communication withsaid refrigeration means for directing a secondary flow of cold airalong a flow path different from the primary flow path to the top of theconveyor, said secondary flow path means including a vertical conduitformed at the center of the conveyor and extending along the conveyor'saxial length; and exit means formed in the housing through which thecold air flows out of the housing after it has been directed along theprimary and secondary flow paths.
 21. The system of claim 20 whereinsaid secondary flow path means causes the secondary flow to pass throughthe vertical conduit, over the top of the conveyor, and downwardlythrough a plurality of upper turns of the conveyor to a position wherethe secondary and primary flows merge.
 22. The system of claim 20further comprising a first means and a second means for controlling theprimary and secondary flows of cold air.
 23. The system of claim 22wherein,said first controlling means includes an adjustable ringdiaphragm for selectively varying the flow of the cold air, saiddiaphragm being positioned between the bottom of the housing and thebottom of the drum; and said second controlling means includes anarcuately segmental plate for selectively varying the flow of the coldair, said plate being associated with said exit means.
 24. The system ofclaim 20 further comprising an internal, rotatable drum for driving saidconveyor and wherein said drum forms said vertical conduit.
 25. In ahelical conveyor system including a helical conveyor with a top and abottom, refrigeration means for providing cold air, and a housingenclosing the conveyor having an exit means, a process for cooling orfreezing a product comprising the steps of:transporting the productusing said conveyor from the bottom to the top of the conveyor;introducing a first flow of cold air to the bottom of the conveyor sothat it flows in a first path under and around the product from thebottom of the conveyor; simultaneously introducing a second flow of coldair to the top of the conveyor so that it flows in a second path overand around the product from the top of the conveyor; and expelling boththe first flow and second flow of cold air from the housing through theexit means after the first flow and second flow have passed by theproduct.
 26. The process of claim 25 further comprising the step ofmerging together the first flow and second flow of cold air immediatelyprior to the step of expelling the first flow and second flow from thehousing.
 27. The process of claim 25 wherein said step of simultaneouslyintroducing a second flow of cold air includes using said second pathincluding a vertical conduit formed at the center of the conveyor andextending along the conveyor's axial length.
 28. The process of claim 25wherein said expelling step includes expelling the first flow and secondflow of cold air through said exit means located intermediate to the topand bottom of said conveyor.
 29. The process of claim 25 furthercomprising the step of controlling air flowing into the housing using aselectively variable device.
 30. The process of claim 25 furthercomprising the step of controlling air flowing out of the housing usinga selectively variable device.